The present invention relates to an objective lens which is used for an optical pick-up apparatus, optical pick-up apparatus and optical information recording reproducing apparatus, and particularly to, by using an objective lens which is an single lens at the definite magnification, an objective lens of the optical pick-up apparatus by which recording and/or reproducing of the optical information recording medium can be conducted, optical pick-up apparatus, and optical information recording reproducing apparatus.
To the optical information recording medium such as a DVD, an optical pick-up apparatus by which the information can be recorded at high density, or reproduced, is developed, and used in various purpose of uses. In such the optical pick-up apparatus, there are various requirements such as the compactness of structure, or the reliability at the time of the environmental temperature change.
In this connection, in the optical pick-up apparatus, as the objective lens by which the information recording light is light converged onto the information recording surface of the optical information recording medium, a material in which the plastic material is a raw material, is used for many cases, because it is advantageous for the mass production. However, in the temperature change of the refractive index, it is well known that the plastic material is about 2 digits larger than the glass material.
Herein, when the environmental temperature of the optical pick-up apparatus having the objective lens formed of the plastic material is increased, and the refractive index of the objective lens is changed, it is well known that the spherical aberration is deteriorated, as the light converging optical system. For example, in the present DVD optical pick-up apparatus, an objective lens of a plastic lens material of the numeral aperture NA is 0.60, and the image formation magnification m=0 is widely spread, however, even when the objective lens is designed so that it becomes no aberration at the focal distance is 3 mm, and the temperature change of the refractive index of the plastic material is dn/dT=xe2x88x920.00012 (/xc2x0 C.), and the refractive index of the plastic material at the wavelength of the light source xcex=650 nm, is n=1.53, when the temperature of the optical pick-up apparatus is increased by 30xc2x0 C. from the room temperature, the refractive index of the objective lens is 1.5264, thereby, the residual aberration of 0.033 xcexrms is generated in the calculation.
Generally, it is said to be necessary that it is suppressed lower than the diffraction limit of the optics (Marxc3xa8chal""s criterion 0.07 arms) in the whole optical system, and because, other than the objective lens, there are various factors to generate the aberration, it is said to be initially important that the aberration generated by the environmental temperature change is suppressed as small as possible.
The spherical aberration deterioration xcex4SA/xcex4T when the refractive index is changed by the environmental temperature change, is expressed by the following expression,
xcex4SA/xcex4Txe2x88x9df(1xe2x88x92m)4NA4xc2x7(dn/dT)/xcex.xe2x80x83xe2x80x83(1)
Where, the focal distance at the infinity object of the objective lens is f, the numerical aperture on the optical information recording medium side is NA, the wavelength of the light source is xcex, the changed amount of the refractive index of the objective lens at the time of the increase of temperature 1xc2x0 C. is dn/dT, and the image formation magnification is m.
In the optical pick-up apparatus to conduct the recording or reproducing of the information onto the high density optical information recording medium such as the recent DVD, there is a tendency that the numerical aperture NA is further increased. Further, in order to secure the compactness of the optical pick-up apparatus, a trial that it is used at the definite magnification and the definite degree is increased, is conducted. On the other hand, according to the expression (1), the more the numerical aperture NA of the objective lens is increased, or for the very objective lens used in the specification in which the definite degree of the optical system is the more increased, it can be understood that the spherical aberration deterioration becomes conspicuous. For example, as described above, at f=3 mm, m=0, when the numerical aperture is increased from 0.60 to 0.85, the aberration is deteriorated in proportional to 4-th power of NA, and the approximation value of the spherical aberration at the time of 30xc2x0 C. temperature rise from the room temperature (for example, 25xc2x0 C.) is 0.12 xcexrms, and it is presumed that it largely exceeds Marxc3xa8chal""s criterion. Further, when the light source such as the blue laser developed recently is used, the further high densification of the information can be expected, however, the light source wavelength xcex is more reduced to the short wavelength thereby, it can be said that the problem of the spherical aberration deterioration to the temperature change is increased to the more severe direction.
To such the problem, from the expression (1) in the same manner, it can be seen that, when the focal distance f is reduced, the spherical aberration deterioration to the temperature change can be suppressed a certain degree. For example, even when the numerical aperture is increased from NA 0.60 to NA 0.85, when the focal distance is decreased to xc2xc, the same temperature characteristic as before the numerical aperture increase can be obtained.
However, when the focal distance f is reduced, the image height characteristic becomes disadvantageous. This is because, when the obtaining of the same image height is tried, the incident angle onto the objective lens is increased. The more the incident angle is increased, the more the astigmatism or coma is deteriorated. Accordingly, in the image height characteristic, it is preferable that the focal distance is larger.
In view of the above problems, the present invention is attained, and the object of the present invention is, even in the optical pick-up apparatus in which the numerical aperture NA is increased, or the light source wavelength is reduced, to provide an objective lens which is an objective lens of a single lens having the good temperature characteristic and by which the whole of the optical system which is well-balanced with the image height characteristic can be made compact, optical pick-up apparatus by using it, and optical information recording reproducing apparatus.
The above object of the invention can be attained by the following structures.
An objective lens for an optical pick-up apparatus described in (1), which has the light source of the wavelength xcex, and objective lens to conduct the recording and/or reproducing of the information by image forming a luminous flux from the light source onto the optical information recording medium, the objective lens for an optical pick-up apparatus is characterized in that: the objective lens is a single lens, and the focal distance f at the infinite object of the objective lens, numerical aperture NA on the optical information recording medium side, wavelength xcex of the light source, changed amount dn/dT of the objective lens refractive index at the time of 1xc2x0 C. increase of the temperature, and image formation magnification m respectively satisfy the following expressions,
0.1 less than f less than 1xe2x80x83xe2x80x83(1)
0.50 less than NA less than 0.90xe2x80x83xe2x80x83(2)
350 nm less than xcex less than 850 nmxe2x80x83xe2x80x83(3)
{fraction (1/10)} less than |m| less than ⅓xe2x80x83xe2x80x83(4)
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.2xe2x80x83xe2x80x83(5)
and when the aberration of the objective lens when the temperature of whole the optical pick-up apparatus is increased from the room temperature (for example, 25xc2x0 C.) by 30xc2x0 C., is xcex4Wtemp, and the aberration at the image height of the objective lens Y=0.02 mm is xcex4Wheight, it is that
0.0xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrmsxe2x80x83xe2x80x83(6).
According to an objective lens described in (1), the focal distance f is reduced corresponding to the increase of the numerical aperture NA, and the reduction to the short wavelength of the light source wavelength xcex, the deterioration of the spherical aberration to the temperature change can be suppressed, however, when the focal distance f is too reduced, because the image height characteristic is deteriorated, when each value is determined within the range satisfying (1)-(6) expressions, an objective lens which is well-balanced with the temperature characteristic and image height characteristic, can be provided. Further, even when it is the high numerical aperture NA, it can be made the definite magnification, thereby it can also be made an optical pick-up apparatus structured compactly and simply in which the luminous flux from the light source is light-converged by using a single objective lens onto the information recording surface of the optical information recording medium.
According to an objective lens for an optical pick-up apparatus described in (2), when the objective lens is structured by the plastic material, because such the plastic material is lighter than the glass material, the increase of the speed of the focusing operation to move the objective lens in the optical axis direction can be attained. Further, because the plastic material is easy for injection molding, the mass production of the objective lens can be conducted with the stable quality.
According to an objective lens for an optical pick-up apparatus described in (3), it is preferable when the objective lens is structured in the both surface aspherical surfaces. Particularly, when the objective lens is structured with the refractive surface, as compared to a case where the objective lens is structured with the diffraction surface, the light amount loss due to the diffraction efficiency is not generated, and it is advantageous in a point in which the transmission light amount is secured.
According to an objective lens for an optical pick-up apparatus described in (4), in the objective lens, which is characterized in that: values of the numerical aperture NA on the optical information recording medium side, wavelength xcex of the light source, changed amount dn/dT of the objective lens refractive index at the time of the temperature 1xc2x0 C. rise, and image formation magnification m, respectively satisfy the following expressions.
0.50 less than NA less than 0.75xe2x80x83xe2x80x83(7)
450 nm less than xcex less than 850 nmxe2x80x83xe2x80x83(8)
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.06.xe2x80x83xe2x80x83(9)
When the numerical aperture NA is larger than 0.50, and the light source wavelength xcex is not larger than 850 nm, it can cope with the optical information recording medium with a comparatively high density, on the one hand, when the numerical aperture NA is not larger than 0.75, and the light source wavelength xcex is larger than 450 nm, the deterioration of the spherical aberration to the temperature change can be suppressed within the range shown by the expression (9).
An objective lens for an optical pick-up apparatus described in (5), is characterized in that the axial thickness d of the objective lens satisfies
0.4 less than d/f less than 1.5xe2x80x83xe2x80x83(10).
When the value d/f exceeds the lower limit value of the expression (10), in the design work, the control of the image height characteristic becomes easy, and on the one hand, when smaller than the upper limit value, when the objective lens is separated from the optical information recording medium, the enough working distance can be secured.
An objective lens for an optical pick-up apparatus described in (6), is characterized in that: when the paraxial radius of curvature of the surface on the light source side of the objective lens is r1, and the refractive index in the wavelength xcex of the objective lens is n, the objective lens satisfies
0.3 less than r1 less than (n(1xe2x88x92m)f) less than 0.5.xe2x80x83xe2x80x83(11)
The present invention particularly relates to the coma component of the image height characteristic. When the expression (11) is satisfied, the correction of so-called sinusoidal condition, as the condition in which the coma is corrected at the time when the luminous flux is obliquely incident onto the objective lens becomes easy.
As can be seen from the expression (11), in the objective lens, it is said to be preferable in the aberration correction that the paraxial radius of curvature r1 on the light source side is reduced in both convex lens. However, thereby, the change of the prospective angle of the aspherical surface on the light source side becomes large as close to the periphery, and the aspherical surface of the surface on the light source side is a large factor to limit the edge thickness. This will be specifically described below.
FIG. 1 is a sectional view typically showing a portion of the objective lens of the present invention. Herein, conventionally, it is conducted that the both surface aspherical surface shape of the objective lens is extended to a position to be connected to a flange portion of the objective lens. However, as the present invention described in (6), when the paraxial radius of curvature r1 is set smaller so as to satisfy the expression (11), as shown by a doted line in FIG. 1, because the prospective angle xcex81 (an angle formed between a tangential line of a intersecting point P3 with the flange portion in the cross section of the aspherical surface on the light source side, and the tangential line of the flange portion at the intersecting point P3) is increased, there is a tendency that the flange thickness t1 is decreased. When the flange thickness t1 is decreased, at the time of molding of the objective lens, the flow of the raw material is badly affected, and there is a problem that the molding trouble is easily generated.
According to the following inventions, such the problem can be eliminated or softened.
An objective lens for an optical pick-up apparatus described in (7) is characterized in that: in a position (herein, P1 shown in FIG. 1) at which the outermost ray (herein, LB1 shown in FIG. 1) of the numerical aperture NA crosses, a linkage area (A shown in FIG. 1) in which the edge thickness of the objective lens is increased, is provided. According to such the invention, the objective lens is a surface shape as shown by the solid line in FIG. 1, and thereby, the prospective angle xcex82 is reduced more than the conventional prospective angle xcex81, and the flange thickness t2 can be more increased, and the productivity of the objective lens can be increased. In this connection, by optimizing the shape of the linkage portion, when the luminous flux passed the linkage area is converted into a flare light which is not related to the image formation, the diaphragm effect can also be provided.
An objective lens for an optical pick-up apparatus described in (8) is characterized in that: in an outside portion in the intersecting direction to the optical axis of the position (herein, P2 shown in FIG. 1) at which the outermost ray (herein, LB2 shown in FIG. 1) of the numerical aperture NA crosses, a linkage area (A shown in FIG. 1) in which the edge thickness of the objective lens is increased, is provided. Because the luminous flux passing the outside portion in the intersecting direction to the optical axis of the position at which the outermost ray of the numerical aperture NA crosses, is not related to the image formation onto the information recording surface of the optical information recording medium, in the design work, as the invention described in (7), the linkage area may be formed directly toward the outside from the position P1 at which the outermost ray intersects, however, in the practice, due to the accuracy of parts, or assembling error, the position at which the outermost ray passes, varies to the designed position. Therefore, as the present invention, at the outside portion in the intersecting direction to the optical axis of the position (P2) at which the outermost ray (LB2) of the numerical aperture NA crosses, when the linkage area in which the edge thickness of the objective lens is increased is provided, even when the intersecting position is varied, the luminous flux passing the inside of the position at which the outermost ray passes is made always to relate to the image formation, and thereby, the transmitted light amount can be effectively secured.
An objective lens for an optical pick-up apparatus described in (9) is characterized in that: in the linkage area, a step is provided in the optical axis direction FIG. 2 is the same sectional view as FIG. 1, which shows a portion of the objective lens of the present invention. In FIG. 2, at the outside in the optical axis right-angled direction from the position (herein, P1 shown in FIG. 2) at which the outermost ray of the numerical aperture NA (herein, LB1 shown in FIG. 2) crosses, the surface on the light source side of such the objective lens (that is, a linkage area) is the step difference (Axe2x80x2 shown in FIG. 2) protruded onto the light source side of the optical axis direction. By conducting as described above, the edge thickness t3 of the objective lens can be secured further largely. In this connection, by optimizing the shape of the step difference, when, for example, the luminous flux which transmits the step difference, is converted into a flare light which is not related to the image formation, the diaphragm effect can also be provided. In this case, the step difference, as shown by a dotted line in FIG. 2, may also be a concave shape to the optical information recording medium side in the optical axis direction.
An objective lens for an optical pick-up apparatus described in (10) is preferable when the difference of the prospective angles of the aspherical shape in the inside and outside in the crossing direction with the optical axis of the linkage area (in FIG. 1, an angle, for example, (xcex81xe2x88x92xcex82), formed between the tangential line with the surface of the lens in the effective diameter at the point P1, and the tangential line of the linkage area at the point P3) is within 20xc2x0. When the prospective angle of the linkage area is too large, it is for the reasons in which it is not preferable that the load onto the top edge portion of the bite becomes too large at the time of the molding working, further, when, at the outside and inside of the linkage area, the molding die is made as the separate members and the objective lens is molded, because the fins are produced in the lens surface, it is not preferable.
An optical pick-up apparatus described in (11) in which it has the light source of the wavelength xcex and an objective lens by which, by image forming the luminous flux from the light source onto the optical information recording medium, the information is recorded and/or reproduced, the optical pick-up apparatus is characterized in that: the objective lens is a single lens, and values of the focal distance f at the infinite object of the objective lens, numerical aperture NA of the optical information recording medium side, the wavelength xcex of the light source, changed amount dn/dT of the objective lens refractive index at the time of the temperature 1xc2x0 C. rise, and image formation magnification m, respectively satisfy the following expressions,
0.1 less than f less than 1xe2x80x83xe2x80x83(1)
xe2x80x830.50 less than NA less than 0.90xe2x80x83xe2x80x83(2)
350 nm less than xcex less than 850 nmxe2x80x83xe2x80x83(3)
{fraction (1/10)} less than |m| less than ⅓xe2x80x83xe2x80x83(4)
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.2xe2x80x83xe2x80x83(5),
and when the residual aberration of the objective lens when the temperature of whole the optical pick-up apparatus is increased from the room temperature (for example, 25xc2x0 C.) by 30xc2x0 C., is xcex4Wtemp, and the residual aberration at the image height of the objective lens Y=0.02 mm is xcex4Wheight,
0.0xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrmsxe2x80x83xe2x80x83(6).
The operational effect of the present invention is the same as the invention described in (1).
An optical pick-up apparatus described in (12) is characterized in that the objective lens is structured by the plastic material. The operational effect of the present invention is the same as the invention described in (2).
An optical pick-up apparatus described in (13) is characterized in that the objective lens is structured by both surface aspherical surfaces. The operational effect of the present invention is the same as the invention described in (3).
An optical pick-up apparatus described in (14) is characterized in that, in the objective lens, values of the numerical aperture NA of the optical information recording medium side, the wavelength xcex of the light source, changed amount dn/dT of the objective lens refractive index at the time of the temperature 1xc2x0 C. rise, and image formation magnification m, respectively satisfy the following expressions,
0.50 less than NA less than 0.75xe2x80x83xe2x80x83(7)
450 nm less than xcex less than 850 nmxe2x80x83xe2x80x83(8)
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.06xe2x80x83xe2x80x83(9).
The operational effect of the present invention is the same as the invention described in (4).
An optical pick-up apparatus described in (15) is characterized in that the axial thickness d of the objective lens satisfies
0.4 less than d/f less than 1.5xe2x80x83xe2x80x83(10).
The operational effect of the present invention is the same as the invention described in (5).
An optical pick-up apparatus described in (16) is characterized in that, when the paraxial radius of curvature of the surface on the light source side of the objective lens is r1, and the refractive index at the wavelength xcex of the objective lens is n, it satisfies
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5xe2x80x83xe2x80x83(11).
The operational effect of the present invention is the same as the invention described in (6).
An optical pick-up apparatus described in (17) is characterized in that the surface of the light source side of the objective lens is provided with, at a position at which the outermost ray of the numerical aperture NA crosses, a linkage area in which the edge thickness of the objective lens is increased. The operational effect of the present invention is the same as the invention described in (7).
An optical pick-up apparatus described in (18) is characterized in that the surface of the light source side of the objective lens is provided with, at the outside portion of the intersecting direction to the optical axis at a position at which the outermost ray of the numerical aperture NA crosses, a linkage area in which the edge thickness of the objective lens is increased. The operational effect of the present invention is the same as the invention described in (8).
An optical pick-up apparatus described in (19) is characterized in that the linkage area is provided with a step difference in the optical axis direction. The operational effect of the present invention is the same as the invention described in (9).
An optical pick-up apparatus described in (20) is characterized in that the difference of the prospective angles of the aspherical surface shape at the inside and outside of the intersecting direction to the optical axis of the linkage area is within 20xc2x0. The operational effect of the present invention is the same as the invention described in (10).
An optical information recording reproducing apparatus described in (21) in which it has the light source of the wavelength xcex and an objective lens by which, by image forming the luminous flux from the light source onto the optical information recording medium, the information is recorded and/or reproduced, the optical information recording reproducing apparatus is characterized in that: the objective lens is a single lens, and values of the focal distance f at the infinite object of the objective lens, numerical aperture NA of the optical information recording medium side, the wavelength xcex of the light source, changed amount dn/dT of the objective lens refractive index at the time of the temperature 1xc2x0 C. rise, and image formation magnification m, respectively satisfy the following expressions,
0.1 less than f less than 1xe2x80x83xe2x80x83(1)
0.50 less than NA less than 0.90xe2x80x83xe2x80x83(2)
350 nm less than xcex less than 850 nmxe2x80x83xe2x80x83(3)
{fraction (1/10)} less than |m| less than ⅓xe2x80x83xe2x80x83(4)
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.2xe2x80x83xe2x80x83(5),
and when the residual aberration of the objective lens when the temperature of whole the optical information recording reproducing apparatus is increased from the room temperature (for example, 25xc2x0 C.) by 30xc2x0 C., is xcex4Wtemp, and the residual aberration at the image height of the objective lens Y=0.02 mm is xcex4Wheight,
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrmsxe2x80x83xe2x80x83(6).
The operational effect of the present invention is the same as the invention described in (1).
An optical information recording reproducing apparatus described in (22) is characterized in that the objective lens is structured by the plastic material. The operational effect of the present invention is the same as the invention described in (2).
An optical information recording reproducing apparatus described in (23) is characterized in that the objective lens is structured by the both surface aspherical surfaces. The operational effect of the present invention is the same as the invention described in (3).
An optical information recording reproducing apparatus described in (24) is characterized in that, in the objective lens, values of the numerical aperture NA of the optical information recording medium side, the wavelength xcex of the light source, changed amount dn/dT of the objective lens refractive index at the time of the temperature 1xc2x0 C. rise, and image formation magnification m, respectively satisfy the following expressions.
0.50 less than NA less than 0.75xe2x80x83xe2x80x83(7)
450 nm less than xcex less than 850 nmxe2x80x83xe2x80x83(8)
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.06xe2x80x83xe2x80x83(9).
The operational effect of the present invention is the same as the invention described in (4).
An optical information recording reproducing apparatus described in (25) is characterized in that the axial thickness d of the objective lens satisfies 0.4 less than d/f less than 1.5 (10). The operational effect of the present invention is the same as the invention described in (5).
An optical information recording reproducing apparatus described in (26) is characterized in that, when the paraxial radius of curvature of the surface on the light source side of the objective lens is r1, and the refractive index at the wavelength xcex of the objective lens is n, it satisfies
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5xe2x80x83xe2x80x83(11).
The operational effect of the present invention is the same as the invention described in (6).
An optical information recording reproducing apparatus described in (27) is characterized in that the surface on the light source side of the objective lens, at the position at which the outermost ray of the numerical aperture NA crosses, is provided with a linkage area in which the edge thickness is increased. The operational effect of the present invention is the same as the invention described in (7).
An optical information recording reproducing apparatus described in (28) is characterized in that the surface on the light source side of the objective lens is, at the outside portion in the intersecting direction to the optical axis of the position at which the outermost ray of the numerical aperture NA crosses, provided with the linkage area in which the edge thickness of the objective lens is increased. The operational effect of the present invention is the same as the invention described in (8).
An optical information recording reproducing apparatus described in (29) is characterized in that the linkage area is provided with a step difference in the optical axis direction. The operational effect of the present invention is the same as the invention described in (9).
An optical information recording reproducing apparatus described in (30) is characterized in that the difference of the prospective angles of the aspherical surface shape at the inner side and the outer side in the intersecting direction to the optical axis of the linkage area is within 20xc2x0. The operational effect of the present invention is the same as the invention described in (10).
(31) An objective lens for use in an optical pickup apparatus which comprises a light source to emit a light flux having a wavelength xcex and the objective lens to focus the light flux on an optical information recording medium for conducting recording or reproducing information, comprising:
the objective lens being a single lens and satisfying the following formulas:
xe2x80x830.1 less than f less than 1
0.70 less than NA less than 0.90
350 nm less than  less than 850 nm
xe2x88x92⅕ less than m less than xe2x88x92{fraction (1/10)}
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.01
1.2 less than d/f less than 1.7
where f is a focal length for an infinite object, NA is a numerical aperture at an optical information recording medium side, xcex is a wavelength of a light flux emitted from the light source, dn/dT represents a change in a refractive index when the temperature changes 1xc2x0 C., m is a magnification and d is an axial thickness; and
the objective lens satisfying the following formula:
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrms
where xcex4Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30xc2x0 C. and xcex4Wheight represents an aberration of the objective lens at an image height Y of 0.002 mm (Y=0.002 mm).
(32) The objective lens of (31), wherein the following formula is satisfied:
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5
where r1 is a paraxial radius of curvature at a light source side and n is a refractive index.
(33) The objective lens of (31), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at a position where an outermost light flux of the numerical aperture NA crosses.
(34) The objective lens of (31), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at an outside in a direction to perpendicular to an optical axis from a position where an outermost light flux of the numerical aperture NA crosses.
(35) The objective lens of (34), wherein a stepped section is provided in a direction of an axial direction at the joint region.
(36) The objective lens of (33), wherein an angle formed by a tangent line tangent to an aspherical surface at an inner end of the joint region and a tangent line tangent to an aspherical surface at an outer end of the joint region is 20xc2x0 or less.
(37) An optical pickup apparatus, comprising:
a light source to emit a light flux having a wavelength xcex; and
an objective lens to focus the light flux on an optical information recording medium for conducting recording or reproducing information;
the objective lens being a single lens and satisfying the following formulas:
0.1 less than f less than 1
0.70 less than NA less than 0.90
350 nm less than xcex less than 850 nm
xe2x88x92⅕ less than m less than xe2x88x92{fraction (1/10)}
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/ less than 0.01
1.2 less than d/f less than 1.7
where f is a focal length for an infinite object, NA is a numerical aperture at an optical information recording medium side, xcex is a wavelength of a light flux emitted from the light source, dn/dT represents a change in a refractive index when the temperature changes 1xc2x0 C., m is a magnification and d is an axial thickness; and
the objective lens satisfying the following formula:
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrms
where xcex4Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30xc2x0 C. and xcex4Wheight represents an aberration of the objective lens at an image height Y of 0.002 mm (Y=0.002 mm).
(38) The optical pickup apparatus of (37), wherein the following formula is satisfied:
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5
where r1 is a paraxial radius of curvature at a light source side and n is a refractive index.
(39) The optical pickup apparatus of (37), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at a position where an outermost light flux of the numerical aperture NA crosses.
(40) The optical pickup apparatus of (37), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at an outside in a direction to perpendicular to an optical axis from a position where an outermost light flux of the numerical aperture NA crosses.
(41) The optical pickup apparatus of (40), wherein a stepped section is provided in a direction of an axial direction at the joint region.
(42) The optical pickup apparatus of (39), wherein an angle formed by a tangent line tangent to an aspherical surface at an inner end of the joint region and a tangent line tangent to an aspherical surface at an outer end of the joint region is 20xc2x0 or less.
(43) An optical information reproducing and/or reproducing apparatus, comprising:
a light source to emit a light flux having a wavelength xcex; and
an objective lens to focus the light flux on an optical information recording medium for conducting recording or reproducing information;
the objective lens being a single lens and satisfying the following formulas:
0.1 less than f less than 1
0.70 less than NA less than 0.90
350 nm less than xcex less than 850 nm
xe2x88x92⅕ less than m less than xe2x88x92{fraction (1/10)}
0.0 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.01
xe2x80x831.2 less than d/f less than 1.7
where f is a focal length for an infinite object, NA is a numerical aperture at an optical information recording medium side, xcex is a wavelength of a light flux emitted from the light source, dn/dT represents a change in a refractive index when the temperature changes 1xc2x0 C., m is a magnification and d is an axial thickness; and
the objective lens satisfying the following formula:
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrms
where xcex4Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30xc2x0 C. and xcex4Wheight represents an aberration of the objective lens at an image height Y of 0.002 mm (Y=0.002 mm).
(44) The optical information reproducing and/or reproducing apparatus of (43), wherein the following formula is satisfied:
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5
where r1 is a paraxial radius of curvature at a light source side and n is a refractive index.
(45) The optical information reproducing and/or reproducing apparatus of (43), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at a position where an outermost light flux of the numerical aperture NA crosses.
(46) The optical information reproducing and/or reproducing apparatus of (43), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at an outside in a direction to perpendicular to an optical axis from a position where an outermost light flux of the numerical aperture NA crosses.
(47) The optical information reproducing and/or reproducing apparatus of (46), wherein a stepped section is provided in a direction of an axial direction at the joint region.
(48) The optical information reproducing and/or reproducing apparatus of (45), wherein an angle formed by a tangent line tangent to an aspherical surface at an inner end of the joint region and a tangent line tangent to an aspherical surface at an outer end of the joint region is 20xc2x0 or less.
(49) An objective lens for use in an optical pickup apparatus which comprises a light source to emit a light flux having a wavelength xcex and the objective lens to focus the light flux on an optical information recording medium for conducting recording or reproducing information, comprising:
the objective lens being a single lens and satisfying the following formulas:
0.1 less than f less than 1
0.70 less than NA less than 0.90
350 nm less than xcex less than 850 nm
xe2x88x92⅕ less than m less than xe2x88x92{fraction (1/10)}
0.01 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.11
1.2 less than d/f less than 1.7
where f is a focal length for an infinite object, NA is a numerical aperture at an optical information recording medium side, xcex is a wavelength of a light flux emitted from the light source, dn/dT represents a change in a refractive index when the temperature changes 1xc2x0 C., m is a magnification and d is an axial thickness; and
the objective lens satisfying the following formula:
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrms
where xcex4Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30xc2x0 C. and xcex4Wheight represents an aberration of the objective lens at an image height Y of 0.002 mm (Y=0.002 mm).
(50) The objective lens of (49), wherein the objective lens comprises a diffractive structure to correct a spherical aberration to an under side at a long wavelength side and satisfies the following formula:   Φ  =            ∑              i        =        1            ∞        ⁢                  c        i            ⁢              h                  2          ⁢          i                    ⁢              xe2x80x83            ⁢              (        mm        )            
(51) The objective lens of (50), wherein the following formula is satisfied:
0.08xe2x89xa6((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.11
(52) The objective lens of (49), wherein the following formula is satisfied:
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5
where r1 is a paraxial radius of curvature at a light source side and n is a refractive index.
(53) The objective lens of (49), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at a position where an outermost light flux of the numerical aperture NA crosses.
(54) The objective lens of (49), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at an outside in a direction to perpendicular to an optical axis from a position where an outermost light flux of the numerical aperture NA crosses.
(55) The objective lens of (54), wherein a stepped section is provided in a direction of an axial direction at the joint region.
(56) The objective lens of (53), wherein an angle formed by a tangent line tangent to an aspherical surface at an inner end of the joint region and a tangent line tangent to an aspherical surface at an outer end of the joint region is 20xc2x0 or less.
(57) An optical pickup apparatus, comprising:
a light source to emit a light flux having a wavelength xcex; and
an objective lens to focus the light flux on an optical information recording medium for conducting recording or reproducing information;
the objective lens being a single lens and satisfying the following formulas:
xe2x80x830.1 less than f less than 1
0.70 less than NA less than 0.90
350 nm less than xcex less than 850 nm
xe2x88x92⅕ less than m less than xe2x88x92{fraction (1/10)}
0.01 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.11
1.2 less than d/f less than 1.7
where f is a focal length for an infinite object, NA is a numerical aperture at an optical information recording medium side, xcex is a wavelength of a light flux emitted from the light source, dn/dT represents a change in a refractive index when the temperature changes 1xc2x0 C., m is a magnification and d is an axial thickness; and
the objective lens satisfying the following formula:
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrms
where xcex4Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30xc2x0 C. and xcex4Wheight represents an aberration of the objective lens at an image height Y of 0.002 mm (Y=0.002 mm).
(58) The optical pickup apparatus of (57), wherein the objective lens comprises a diffractive structure to correct a spherical aberration to an under side at a long wavelength side and satisfies the following formula:   Φ  =            ∑              i        =        1            ∞        ⁢                  c        i            ⁢              h                  2          ⁢          i                    ⁢              xe2x80x83            ⁢              (        mm        )            
(59) The optical pickup apparatus of (58), wherein the following formula is satisfied:
0.08 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.11
(60) The optical pickup apparatus of (57), wherein the following formula is satisfied:
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5
where r1 is a paraxial radius of curvature at a light source side and n is a refractive index.
(61) The optical pickup apparatus of (57), wherein a light source side surface of the objective lens is provided with a joint region to make a-thickness of a peripheral portion of the objective lens thicker at a position where an outermost light flux of the numerical aperture NA crosses.
(62) The optical pickup apparatus of (57), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at an outside in a direction to perpendicular to an optical axis from a position where an outermost light flux of the numerical aperture NA crosses.
(63) The optical pickup apparatus of (62), wherein a stepped section is provided in a direction of an axial direction at the joint region.
(64) The optical pickup apparatus of (61), wherein an angle formed by a tangent line tangent to an aspherical surface at an inner end of the joint region and a tangent line tangent to an aspherical surface at an outer end of the joint region is 20xc2x0 or less.
(65) An optical information reproducing and/or reproducing apparatus, comprising
a light source to emit a light flux having a wavelength xcex; and
an objective lens to focus the light flux on an optical information recording medium for conducting recording or reproducing information;
the objective lens being a single lens and satisfying the following formulas:
0.1 less than f less than 1
0.70 less than NA less than 0.90
350 nm less than xcex less than 850 nm
xe2x88x92⅕ less than m less than xe2x88x92{fraction (1/10)}
0.01 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.11
xe2x80x831.2 less than d/f less than 1.7
where f is a focal length for an infinite object, NA is a numerical aperture at an optical information recording medium side, xcex is a wavelength of a light flux emitted from the light source, dn/dT represents a change in a refractive index when the temperature changes 1xc2x0 C., m is a magnification and d is an axial thickness; and
the objective lens satisfying the following formula:
0.0 xcexrms less than xcex4Wtemp+xcex4Wheight less than 0.07 xcexrms
where xcex4Wtemp represents an aberration of the objective lens when an ambient temperature of the optical pickup apparatus is changed from a room temperature by 30xc2x0 C. and xcex4Wheight represents an aberration of the objective lens at an image height Y of 0.002 mm (Y=0.002 mm).
(66) The optical information reproducing and/or reproducing apparatus of (65), wherein the objective lens comprises a diffractive structure to correct a spherical aberration to an under side at a long wavelength side and satisfies the following formula:   Φ  =            ∑              i        =        1            ∞        ⁢                  c        i            ⁢              h                  2          ⁢          i                    ⁢              xe2x80x83            ⁢              (        mm        )            
(67) The optical information reproducing and/or reproducing apparatus of (66), wherein the following formula is satisfied:
0.08 less than ((1xe2x88x92m)NA)4xc3x97fxc3x97|dn/dT|/xcex less than 0.11
(68) The optical information reproducing and/or reproducing apparatus of (65), wherein the following formula is satisfied:
0.3 less than r1/(n(1xe2x88x92m)f) less than 0.5
where r1 is a paraxial radius of curvature at a light source side and n is a refractive index.
(69) The optical information reproducing and/or reproducing apparatus of (65), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at a position where an outermost light flux of the numerical aperture NA crosses.
(70) The optical information reproducing and/or reproducing apparatus of (65), wherein a light source side surface of the objective lens is provided with a joint region to make a thickness of a peripheral portion of the objective lens thicker at an outside in a direction to perpendicular to an optical axis from a position where an outermost light flux of the numerical aperture NA crosses.
(71) The optical information reproducing and/or reproducing apparatus of claim 70), wherein a stepped section is provided in a direction of an axial direction at the joint region.
(72) The optical information reproducing and/or reproducing apparatus of (69), wherein an angle formed by a tangent line tangent to an aspherical surface at an inner end of the joint region and a tangent line tangent to an aspherical surface at an outer end of the joint region is 20xc2x0 or less.
In the present specification, the objective lens indicates, in the narrow meaning, a lens having the light converging action which is arranged in opposite to the optical information recording medium at the position of the most optical information recording medium side, in the condition in which the optical information recording medium is loaded into the optical pick-up apparatus, and in the broad meaning, a lens by which it can be operated by the actuator together with the lens, at least in its optical axis direction. Accordingly, in the present specification, the numerical aperture NA of the optical information recording medium side (image side) of the objective lens indicates the numerical aperture NA of the lens surface positioned on the most optical information recording medium side of the objective lens. Further, in the present specification, the necessary numerical aperture NA shows the numerical aperture regulated by the regulation of respective optical information recording medium, or the numerical aperture of the objective lens of the diffraction limit performance by which, to respective optical information recording medium, corresponding to the wavelength of the using light source, a spot diameter necessary for conducting the recording or reproducing of the information can be obtained.